1. Field of the Invention
The present invention is directed generally to a wafer cutting chuck used in conjunction with a wafer cutting blade for cutting a semiconductor wafer into dice and, more particularly, to a chuck which reduces wear and damage to a cutting blade, and an associated method.
2. Description of the Background
Integrated circuits have touched almost every aspect of society, such as children's games and toys, engine computers in automobiles, personal computers in homes and offices, and controllers in industrial processes. Better ways to fabricate integrated circuits are constantly being sought.
Integrated circuits are fabricated on semiconductor wafers, and the each wafer typically contains between 50 and 1,000 individual integrated circuits. Between the integrated circuits are spaces, known as "street indices", which separate the individual integrated circuits on the wafer. Street indices are as small as possible, and are typically 4 mil to 6 mil wide. In a process known as "dicing", wafers are cut along the street indices to form separate integrated circuits, known as "dice". A street index which has been cut is known as,a "street". When the dicing process is completed, the streets form a grid which defines the dice cut from the wafer.
The dicing process is performed with wafer spindle and blade assemblies having circular cutting blades. The design and use of wafer spindle and blade assemblies and cutting blades are well known in the prior art, and such devices may be obtained from Disco Hi Tech America, Inc., located in Santa Clara, Calif. The cutting blades are about one mil thick and spin at speeds between 30,000 and 60,000 revolutions per minute. Cutting blades are often nickel-plated with a diamond grit cutting edge to insure smooth, clean cuts, with minimal fraying and splintering.
Wafers are placed on a smooth, level surface, known as a "cutting chuck", where they are diced by a cutting blade. During the dicing process, a cutting blade will occasionally protrude below a wafer and into the underlying cutting chuck. The contact between the cutting blade and cutting chuck accelerates the wear on the cutting blade, and often breaks the cutting blade and results in damage to the cutting chuck.
It is well known in the prior art to use a wafer frame and adhesive tape to maintain dice in place during the dicing process. The wafer frame is generally flat and defines an opening which is larger than the wafer. The adhesive tape is attached to the wafer frame and stretched across the opening. A wafer is secured to the adhesive tape within the opening, and the frame is secured, for example by a vacuum, to the cutting chuck for dicing. After the dice have been cut, the frame, along with the adhesive tape and the dice, are removed from the cutting chuck. The dice are separated from the adhesive tape, the adhesive tape is removed from the frame, and the frame is reused. The adhesive tape is known as "sticky back" and is usually a polymer-based film, such as poly-vinyl chloride ("PVC"), with an adhesive coating on one side. The adhesive tape is usually about 3 mils thick. The dice stick to the adhesive, so that when the wafer is cut the dice remain in place on the cutting chuck and are not scattered. Because a cutting blade extends slightly below the wafer, the cutting blade is exposed to the adhesive tape. Unfortunately, the adhesive binds to the cutting blade, causing accelerated blade wear and "gumming-up" the cutting blade. The gumming-up of the cutting blade reduces the effectiveness of the blade, increases friction between the cutting blade and the wafer resulting in increased heat build up on the blade, and causes binding of the cutting blade, potentially breaking it. Those factors reduce the rate at which the cutting blade can be moved across a wafer, thereby increasing the amount of time required to dice a wafer.
Unfortunately, the accelerated wear and damage caused to cutting blades from impinging upon the chuck and exposure to the adhesive requires that they be replaced after dicing only about five or six wafers. Worn cutting blades lack the sharpness to cleanly cut a wafer, and cutting blades exposed to adhesives have rough sides and an irregular cutting surface formed from hardened adhesive picked up during previous cuts of a wafer. The continued use of a worn cutting blade may result in damaged or destroyed wafers caused by the cutting blade sailing catastrophically and spraying debris across the wafer. Replacing cutting blades is expensive, however, not only in terms of the costs of the cutting blade, but also in terms of down time of the dicing process and interruption of the fabrication process while an old cutting blade is being removed and a new cutting blade is being installed.
Thus, the need exists for an improved cutting chuck which reduces the amount of wear and damage to a cutting blade. In particular, the need exists for a cutting chuck which does not interfere with a cutting blade during dicing, and which reduces or prevents contact between a cutting blade and adhesives used to secure a wafer onto the cutting chuck.